1. Field of the Invention
The present invention is directed to a method and apparatus for aligning depth images with projection overlays and, more particularly, to aligning image lines of a lenticular print with lenticules of a lenticular overlay or faceplate using alignment lines adjacent to the print, printed parallel to the image lines and projected through one or more lenticules of the lenticular overlay or faceplate.
2. Description of the Related Art
A lenticular image fixed in a recording media, such as a photographic print or transparency media or displayed on a CRT display, comprises image lines interleaved from plural images. The image lines can be created by plural scan lines of a printer or display. A lenticular overlay or faceplate, including plural lenticules, when placed over the media and in proper alignment with the image lines projects the images at different viewing angles providing a picture with a sense of depth. Generating lenticular images in a recording media using a scan printer is described in the related application mentioned previously.
Film writers like the Symbolic Sciences International Fire 1000 and the Light Valve Technology Model 1620B available from Light Valve Technology a subsidiary of Eastman Kodak, which is a preferred printer, are controlled by computers to generate lines of pixels (also known as scan lines) by affecting a relative motion between a microscopically small light writing dot and the photographic media upon which the image is being recorded. The light level of the writing dot is modulated in accordance with pixel data in a computer image file. Since the data which modulates the light level is delivered out of the image storage device of the printer at the speed of the printer's computer clock, this is also referred to as the fast scan direction. After each scan line of information has been so written, the writing head and photographic media are translated relative to each other to a new scan line position parallel and adjacent to the written scan line. This motion only occurs after a full line of data in the fast scan direction has been recorded and is referred to as the slow scan direction. Generally, when lenticular prints are viewed, the orientation of the lenticules is vertical, i.e. the axes of the cylindrical lens segments run up and down relative to the viewer. As the viewer moves in a lateral direction, new perspective views are seen by each eye, thereby creating not only an autostereoscopic depth image, but some look-around effect as well. Each perspective view is a result of a set of exposed image or scan lines, one behind each lenticule, the composite of which comprises the entire view. As the eye is moved laterally, a new set of scanned lines becomes visible as a composite which in turn comprises the new perspective view.
It is possible to generate lenticular prints by scan printing across the sets of views that represent the entire horizontal angular range of the perspectives, but the dynamic range of image density changes along vertical scene lines are only a result of scene changes while the dynamic range along horizontal scene lines result from both scene changes and perspective changes. Therefore, to avoid taxing the film writer's recording dynamic range of density (which can be affected by the temporal frequency of the data flow), orienting the fast scan direction of the film writer with the vertical scene direction is preferable.
The variance in density and color differences between adjacent scan lines when generated as described in the previous paragraph is approximately equivalent for changes in perspective from picture 1 to picture 2, to that of picture 2 to picture 3, and so on to picture n-1 and picture n (where n is the number of scan lines under any given lenticule); but increases rapidly when the change in perspective from picture n to picture 1 is reached. This is not surprising because the angular differences between adjacent perspectives is substantially a small, constant amount, while the angular change from picture 1 to picture n is the entire horizontal angular range of perspectives.
This condition can also be described from the vantage of the print viewer. When carefully observed in a sequential fashion from view 1 to view n, image changes are preferably small and gradual as one might expect when viewing a real scene and slowly moving the head in a lateral direction. However, when moving past view n, suddenly view 1 of an adjacent lenticule becomes visible which constitutes an abrupt image or shift change back to the initial perspective. This effect is termed image break and represents a point in the angular space in front of a lenticular print where the primary image is no longer seen, and a satellite image is seen. The satellite images are equally valid representations of the object scene and serve to increase the total range of angular space that multiple viewers can simultaneously enjoy in a given lenticular picture. However, it is important that the primary image be properly centered to the lenticular array and that the scan lines and the lenticular axes be parallel to each other. If the primary image is not centered, it's projection space will not be centered on a normal to the print surface which leads to viewer confusion as to from where to view the print. If the scan lines are tilted slightly with respect to the lenticule axes, the image break is seen as an angled Moire pattern superimposed over the area image which detracts from the enjoyment of the display. As a result, a need exists for a method of accurately aligning the scan lines with the lenticules of the lenticular overlay.